Body-bias voltage routing structures

ABSTRACT

Body-bias voltage routing structures. In an embodiment, doped well structures distribute body biasing voltages to a plurality of body biasing wells of an integrated circuit.

RELATED APPLICATIONS

This application is a Continuation of co-pending, commonly-owned U.S.patent application Ser. No. 14/160,200, now U.S. Pat. No. 9,406,601,filed Jan. 21, 2014, which in turn was a Continuation of U.S. patentapplication Ser. No. 12/140,197, now U.S. Pat. No. 8,633,547, filed Jun.16, 2008, which in turn was a Divisional Application of U.S. patentapplication Ser. No. 10/816,269, now U.S. Pat. No. 7,388,260, filed onMar. 31, 2004, to Masleid et al., titled “Structure for Spanning Gap inBody-Bias Voltage Routing Structure.” All such applications areincorporated herein by reference in their entirety.

FIELD OF INVENTION

The present invention generally relates to semiconductor chips andMOSFETS (metal oxide semiconductor field effect transistors). Moreparticularly, the present invention relates to the field of spanninggaps in the body-bias voltage routing structure to the MOSFETS.

BACKGROUND

Generation of the physical layout of a semiconductor device havingMOSFETS (metal oxide semiconductor field effect transistors) formed on asemiconductor substrate is a challenging task. An extensive amount oftime and resources are spent during the creation of the physical layout.However, consumption of resources can be minimized if new physicallayouts utilize substantial portions of existing physical layouts. Forexample, a new physical layout having MOSFETS that are body-biased wouldbe less expensive to generate if an existing physical layout havingMOSFETS without body-bias is utilized and modified according to theneeds of the new physical design. Unfortunately, this process ofmodifying the existing physical layout typically requires forming anadditional routing layer for the body-bias voltage on the surface of thesemiconductor device, creating a serious issue since the existingphysical layout utilizes most, if not all, available surface area.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to structures forbody-bias voltage routing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention. Unless otherwise noted, the drawings are not drawn to scale.

FIG. 1 illustrates a top view of a pFET formed in an N-well inaccordance with an embodiment of the present invention, showing the pFEThaving a body-bias voltage Vnw applied to its bulk/body B terminal.

FIG. 2A illustrates the relative positioning of an N-well and a deepN-well region beneath a surface of a semiconductor device in accordancewith an embodiment of the present invention.

FIG. 2B illustrates a side view of a deep N-well region coupled toN-well_1 and N-well_2 in accordance with an embodiment of the presentinvention, showing the routing of the body-bias voltage.

FIG. 3A illustrates a top view of N-well_1 and N-well_2 in accordancewith an embodiment of the present invention.

FIG. 3B illustrates a top view of N-well_3 and N-well_4 in accordancewith an embodiment of the present invention.

FIG. 4 illustrates a top view of a semiconductor device in accordancewith an embodiment of the present invention, showing multiple areas eacharea corresponding to a separate layout pattern for the deep N-well.

FIG. 5A illustrates a top view of multiple diagonal deep N-well (DDNW)regions forming a diagonal sub-surface mesh structure in accordance withan embodiment of the present invention.

FIG. 5B illustrates a top view of multiple N-wells and multiple diagonaldeep N-well (DDNW) regions forming a diagonal sub-surface mesh structurein accordance with an embodiment of the present invention.

FIG. 6A illustrates a top view of multiple diagonal deep N-well (DDNW)regions forming a first diagonal sub-surface strip structure inaccordance with an embodiment of the present invention.

FIG. 6B illustrates a top view of multiple diagonal deep N-well (DDNW)regions forming a second diagonal sub-surface strip structure inaccordance with an embodiment of the present invention.

FIG. 7 illustrates a top view of multiple axial deep N-well (ADNW)regions forming an axial sub-surface mesh structure in accordance withan embodiment of the present invention.

FIG. 8A illustrates a top view of multiple axial deep N-well (ADNW)regions forming a first axial sub-surface strip structure in accordancewith an embodiment of the present invention.

FIG. 8B illustrates a top view of multiple axial deep N-well (ADNW)regions forming a second axial sub-surface strip structure in accordancewith an embodiment of the present invention.

FIG. 9A illustrates a top view of a semiconductor device, showing afirst deep N-well mesh structure, a second deep N-well mesh structure,and an isolation structure formed between these deep N-well meshstructures to create a gap between these deep N-well mesh structures inaccordance with an embodiment of the present invention.

FIG. 9B illustrates a top view of a semiconductor device, showing a deepN-well mesh structure and an isolation structure that creates a gap inthe deep N-well mesh structure in accordance with an embodiment of thepresent invention.

FIG. 10 illustrates a cross-sectional view of the semiconductor deviceof FIG. 9A along line A-B in accordance with an embodiment of thepresent invention.

FIG. 11A illustrates a top view of semiconductor device of FIG. 9A,showing a metal structure for spanning the isolation structure inaccordance with an embodiment of the present invention.

FIG. 11B illustrates a top view of semiconductor device of FIG. 9B,showing a metal structure for spanning the isolation structure inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims. Furthermore, in the following detaileddescription of the present invention, numerous specific details are setforth in order to provide a thorough understanding of the presentinvention. However, it will be recognized by one of ordinary skill inthe art that the present invention may be practiced without thesespecific details.

Although the following description of the present invention will focuson routing a body-bias voltage to pFETS (or p-type MOSFETS) formed insurface N-wells via a conductive sub-surface region of N-type dopingwhen a p-type substrate and an N-well process are utilized, the presentinvention is equally applicable to routing a body-bias voltage to nFETS(or n-type MOSFETS) formed in surface P-wells via a conductivesub-surface region of P-type doping when an n-type substrate and aP-well process are utilized.

Body-Bias Voltage Routing Structures

FIG. 1 illustrates a top view of a pFET 50 (or p-type MOSFET) formed inan N-well_10 when a p-type substrate and an N-well process are utilizedin accordance with an embodiment of the present invention, wherein pFET50 has a body-bias voltage Vnw applied to its bulk/body B terminal. Asdepicted in FIG. 1, pFET 50 has gate G, drain D (p-type doping), sourceS (p-type doping), and bulk/body B terminals. In particular, bulk/body Bterminal is coupled to N-well_10. Hence, a voltage applied to bulk/bodyB terminal is received by N-well_10. The N-well has an n-type doping.Regions of a semiconductor device that are doped with an n-type dopanthave one type of conductivity while regions that are doped with a p-typedopant have another type of conductivity. Typically, various dopantconcentrations are utilized in different regions of the semiconductordevice.

The pFET 50 is body-biased to influence its performance. Withoutbody-biasing, the source S and bulk/body B terminals may be coupledtogether. With body-biasing, the source S and bulk/body B terminals arenot coupled together. Body-biasing enables controlling the potentialdifference between the source S and bulk/body B terminals of the pFET50, providing the ability to electrically tune the threshold voltagelevel of the pFET 50.

In the case of body-biasing, bulk/body B terminal receives a body-biasvoltage Vnw. As described above, bulk/body B terminal represents aconnection to N-well 10. Thus, the body-bias voltage Vnw is applied toN-well_10.

Instead of generating an entire new physical layout for a semiconductordevice to support pFET 50 having the body-bias voltage Vnw, an existingphysical layout can be modified. In particular, the existing physicallayout is modified by including a deep N-well region to route thebody-bias voltage Vnw to N-wells 10 which generally are separated byP-well regions, wherein deep N-well represents a conductive sub-surfacewell layer that is beneath the surface N-well_10. This avoids having tocreate another surface routing layer on a surface of the semiconductordevice that does not have much free surface area for additional routing.

Several layout patterns for the deep N-well region are described herein.These layout patterns facilitate routing the body-bias voltage in thesemiconductor device. The layout patterns include a diagonal sub-surfacemesh structure (see FIG. 5A), an axial sub-surface mesh structure (seeFIG. 7), a diagonal sub-surface strip structure (see FIG. 6A and FIG.6B), and an axial sub-surface strip structure (see FIG. 8A and FIG. 8B).A particular layout pattern is selected for an area of the semiconductordevice according to several factors as will be described below. Once theparticular layout pattern is selected, the layout for the deep N-wellregion can be generated in an automated manner.

The body-bias voltage Vnw is routed to the N-wells via one or more deepN-well regions (which are conductive sub-surface well layers) as opposedto surface metal layers. In one embodiment, the deep N-well region is adiagonal deep N-well region as will be described below. In anotherembodiment, the deep N-well region is an axial deep N-well region aswill be described below. The advantage of this approach is that whiletypically there is little or no room on the densely packed surface areaof the semiconductor device for extra metal routing layers, the areabeneath the surface of the semiconductor device is often underutilizeddue to the fact that routing signals through wells is generallyprohibited by the poor frequency response and potentially unfavorableresistance of the wells. In the present invention, rather than carryingsignals, the deep N-well regions serve to hold and distribute thebody-bias voltage Vnw.

FIG. 2A illustrates the relative positioning of an N-well_10 (also knownas a surface N-well) and a deep N-well region 20 beneath a surface 70 ofa semiconductor device in accordance with an embodiment of the presentinvention. N-well_10 is formed beneath surface 70 of the semiconductordevice and has an N-type doping. Deep N-well region 20 is formed beneathN-well_10 such that deep N-well region 20 and N-well_10 share asub-surface conductive boundary 25 that allows deep N-well region 20 tofunction like a conductive sub-surface routing layer for routing thebody-bias voltage Vnw to the N-wells. That is, deep N-well region 20contacts N-well_10 along the sub-surface conductive boundary 25.Moreover, deep N-well region 20 is buried under surface 70 of thesemiconductor device. Deep N-well region 20 has an N-type doping. Itshould be understood that if an n-type substrate and a P-well processwere utilized, a deep well of P-type doping would be utilized tofunction as a conductive sub-surface routing layer for routing thebody-bias voltage to the surface P-wells.

The dimensions and size of the sub-surface conductive boundary 25determine the resistance of the conductive path between N-well_10 anddeep N-well region 20. As the size of sub-surface conductive boundary 25is increased, the resistance of sub-surface conductive path betweenN-well_10 and deep N-well region 20 is lowered to create alow-resistance conductive path.

FIG. 2B illustrates a side view of a deep N-well region coupled toN-well_1 and N-well_2 in accordance with an embodiment of the presentinvention, showing the routing of the body-bias voltage. As illustratedin FIG. 2B, there is a first sub-surface conductive boundary 396 betweenN-well_1 and deep N-well region 310. Moreover, there is a secondsub-surface conductive boundary 397 between N-well_2 and deep N-wellregion 310. Surface N-well_1 has a PFET 370. Also, surface N-well_2 hasa PFET 370. The P-well region has an NFET 380 and separates N-well_1 andN-well_2. The body-bias voltage Vnw is routed to N-well_1 and N-well_2via the first and second sub-surface conductive boundaries 396 and 397.

A top view of N-well_1 and N-well_2 in accordance with an embodiment ofthe present invention is illustrated in FIG. 3A. As depicted in FIG. 3A,N-well_1 and N-well_2 have an axial orientation. That is, N-well_1 andN-well_2 are positioned along an axis (e.g., x-axis). N-well_1 andN-well_2 have an N-type doping. The body-bias voltage Vnw is routed toN-well_1 and N-well_2 so that pFETs 370 can be body-biased via the deepN-well region. Thus, a contact for the body-bias voltage Vnw can beformed wherever there is free surface area, such as above N-well_1,N-well_2, or deep N-well region. Since N-well_1 and N-well_2 areseparated by a P-type region or P-well region 385 on which nFETS 380 areformed, the layout pattern of the deep N-well is carefully selected toavoid isolating the P-type region or P-well region 385 on which nFETS380 are formed, allowing the formation of conductive paths betweenP-well region 385 and a sub-surface layer (e.g., doped with P-typematerial) that is formed beneath the deep N-well region. Here, N-well_1and N-well_2 are separated by the length d.

FIG. 3B illustrates a top view of N-well_3 and N-well_4 in accordancewith an embodiment of the present invention. As depicted in FIG. 3B,N-well_3 and N-well_4 also have an axial orientation. That is, N-well_3and N-well_4 are positioned along an axis (e.g., y-axis). N-well_3 andN-well_4 have an N-type doping. The body-bias voltage Vnw is routed toN-well_3 and N-well_4 so that pFETs 370 can be body-biased via the deepN-well region. Thus, a contact for the body-bias voltage Vnw can beformed wherever there is free surface area, such as above N-well_3,N-well_4, or deep N-well region. Since N-well_3 and N-well_4 areseparated by a P-type region or P-well region 385 on which nFETS 380 areformed, the layout pattern of the deep N-well is carefully selected toavoid isolating the P-type region or P-well region 385 on which nFETS380 are formed, allowing the formation of conductive paths betweenP-well region 385 and a sub-surface layer (e.g., doped with P-typematerial) that is formed beneath the deep N-well region. Here, N-well_3and N-well_4 are separated by the length m.

FIG. 4 illustrates a top view of a semiconductor device 400 inaccordance with an embodiment of the present invention, showing multipleareas 401-404, each area corresponding to a separate layout pattern forthe deep N-well. In general, the layout distribution of surface N-wellsand surface P-type regions or P-wells on semiconductor device 400 ischaracterized by particular patterns. Semiconductor device 400 can bedivided according to these particular patterns into multiple areas401-404. Alternatively, semiconductor device 400 may have a singlelayout distribution of surface N-wells and surface P-type regions orP-wells.

Once the layout patterns of the surface N-wells and surface P-typeregions or P-wells are recognized, a layout pattern for the deep N-wellregion can be selected for the particular area. The layout patterns forthe deep N-well region include a diagonal sub-surface mesh structure(see FIG. 5A), an axial sub-surface mesh structure (see FIG. 7), adiagonal sub-surface strip structure (see FIG. 6A and FIG. 6B), and anaxial sub-surface strip structure (see FIG. 8A and FIG. 8B). The factorsevaluated in selecting a particular layout pattern for the deep N-wellregion include: providing a low resistance conductive path for routingthe body-bias voltage and avoiding the isolation of the P-type region orP-well region 385 (FIGS. 3A and 3B) on which nFETS 380 are formed toallow the formation of conductive paths between P-well region 385 and asub-surface layer (e.g., doped with P-type material) that is formedbeneath the deep N-well region.

Moreover, the primary factors in determining which particular layoutpattern for the deep N-well region to use are the type of layout pattern(e.g., horizontal strips or vertical strips) of surface N-wells (seeFIGS. 3A and 3B)) and the separation length between adjacent surfaceN-wells (e.g., separation length d in FIG. 3A, and separation length min FIG. 3B). Since each type of layout pattern of surface N-wells (seeFIGS. 3A and 3B) exhibits unique characteristics, a layout pattern forthe deep N-well region is selected that is appropriate for thosecharacteristics exhibited by the layout pattern of the surface N-wells.Within each area 401-404, adjustments to the layout pattern of the deepN-well can be made to overcome any violations of the layout design rulesand to improve the factors described above.

FIG. 5A illustrates a top view of multiple diagonal deep N-well (DDNW)regions forming a diagonal sub-surface mesh structure 500 in accordancewith an embodiment of the present invention. Rather than having acontinuous planar layer for the deep N-well, multiple diagonal deepN-well (DDNW) regions are patterned according to a layout pattern. Asdepicted in FIG. 5A, each diagonal deep N-well region 510A-510E and512A-512D has a strip shape, is formed beneath the surface N-well layerof a semiconductor device, and is doped with an N-type material.Diagonal deep N-well regions 510A-510E are formed in a first parallelorientation while diagonal deep N-well regions 512A-512D are formed in asecond parallel orientation. The first parallel orientation and thesecond parallel orientation are orthogonal to each other and arediagonal (or slanted) with respect to N-well regions of FIGS. 3A and 3B.In an embodiment, the first parallel orientation and N-well regions ofFIGS. 3A and 3B form an angle that is approximately 45 degrees.Additionally, in an embodiment, the second parallel orientation andN-well regions of FIGS. 3A and 3B form an angle that is approximately 45degrees. Thus, diagonal deep N-well regions 510A-510E and 512A-512D forma diagonal sub-surface mesh structure 500 for routing the body-biasvoltage Vnw to the N-well regions so that pFETs can be body-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and diagonal sub-surface meshstructure 500 to provide a plurality of sub-surface conductive pathsbetween N-well regions without isolating the P-well region locatedbetween N-wells. That is, diagonal sub-surface mesh structure 500contacts N-wells along the sub-surface conductive boundaries (e.g.,sub-surface conductive boundary 25 (FIG. 2A) and sub-surface conductiveboundaries 396 and 397 (FIG. 2B)).

The orientation of diagonal sub-surface mesh structure 500 is diagonalwith respect to the orientation of N-well regions of FIGS. 3A and 3B. Inan embodiment, diagonal sub-surface mesh structure 500 is rotatedapproximately 45 degrees with respect to N-well regions of FIGS. 3A and3B. It should be understood that diagonal sub-surface mesh structure 500can have other configurations. For example, gaps 540A and 540B betweenadjacent diagonal deep N-well regions can vary in size. Moreover, theratio of diagonal deep N-well regions to gap area 430 can vary.

Additionally, diagonal sub-surface mesh structure 500 enables nFETS(n-type MOSFETS) 380 (FIGS. 3A and 3B) to be body-biased in any mannerby preventing isolation of a P-type region or P-well region 385 (FIGS.3A and 3B) on which nFETS 380 are formed. Gap area 530 between diagonaldeep N-well regions 510A-510E and 512A-512D prevents isolation of P-wellregion 385 and enables a conductive path between P-well region 385 and asub-surface layer that is beneath diagonal deep N-well regions 510A-510Eand 512A-512D. In an embodiment, the area of diagonal sub-surface meshstructure 500 is equally divided between diagonal deep N-well regions(e.g., 510A-510E and 512A-512D) and gap area 530.

As discussed above, a contact for the body-bias voltage Vnw can beformed wherever there is free space, such as above N-well regions orabove diagonal deep N-well regions 510A-510E and 512A-512D. Moreover,the location and size of the diagonal sub-surface mesh structure 500 isbased on the distribution of the N-wells and the P-type regions orP-wells, wherein the goal is to provide low resistance conductive pathsfor the body-bias voltage Vnw.

However, the size of diagonal sub-surface mesh structure 500 shouldavoid isolating P-type regions or P-wells 385 (FIGS. 3A and 3B) fromsub-surface layers that are formed beneath diagonal deep N-well regions510A-510E and 512A-512D. Moreover, gap area 530 is sized so as toprovide a low-resistance conductive path between P-type regions orP-wells 385 and a sub-surface layer that is formed beneath diagonal deepN-well regions, wherein the greater the gap area 530 the lower theresistance of this conductive path. Additionally, lateral diffusion andlateral depletion can further reduce gap area 530, potentiallypinching-off this conductive path between P-type regions or P-wells 385and a sub-surface layer that is formed beneath diagonal deep N-wellregions. As a solution to this situation, gaps 540A and 540B betweenadjacent diagonal deep N-well regions are made sufficiently wide toavoid pinching-off this conductive path between P-type regions orP-wells 385 and a sub-surface layer that is formed beneath diagonal deepN-well regions. Yet, as the number and size of the diagonal deep N-wellregions are increased, the resistance of the conductive path for routingthe body-bias voltage Vnw is decreased because there are larger and moresub-surface conductive boundaries between N-well regions and diagonaldeep N-well regions. Hence, there is a trade-off between gap area 530and diagonal deep N-well regions in each design situation.

FIG. 5B illustrates a top view of multiple N-wells (e.g., N-well_1 andN-well_2) and multiple diagonal deep N-well (DDNW) regions forming adiagonal sub-surface mesh structure in accordance with an embodiment ofthe present invention. Here, diagonal deep N-well regions 410A and 410Bare orthogonal to diagonal deep N-well regions 412A, 412B, and 412C.Thus, diagonal deep N-well regions 412A, 412B, 412C, 410A, and 410B forma diagonal sub-surface mesh structure 490 for routing the body-biasvoltage Vnw to N-well_1 and N-well_2 so that pFETs 470 can bebody-biased. In an embodiment, the area of diagonal sub-surface meshstructure 490 is equally divided between diagonal deep N-well regionsand gap area 430.

It should be understood that diagonal sub-surface mesh structure 490 canhave other configurations. Gaps 440A and 440B between adjacent diagonaldeep N-well regions can vary in size. Moreover, the ratio of diagonaldeep N-well regions to gap area 430 can vary. The regions 495 betweendiagonal deep N-well regions prevent isolation of P-well region 485 andenable a conductive path between P-well region 485 and a sub-surfacelayer that is beneath diagonal deep N-well regions 412A, 412B, 412C,410A, and 410B.

A top view of multiple diagonal deep N-well (DDNW) regions forming afirst diagonal sub-surface strip structure 600A in accordance with anembodiment of the present invention is illustrated in FIG. 6A. In thislayout pattern, each diagonal deep N-well region 610A-610D has a stripshape, is formed beneath the surface N-well layer of a semiconductordevice, and is doped with an N-type material. Diagonal deep N-wellregions 610A-610D are formed in a first parallel orientation. The firstparallel orientation is diagonal (or slanted) with respect to surfaceN-well regions (e.g., N-well_A, N-well_B, and N-well_C). In anembodiment, the first parallel orientation and the N-well regions forman angle that is approximately 45 degrees. In this case, the combinationof surface N-well regions (e.g., N-well_A, N-well_B, and N-well_C) andthe first diagonal sub-surface strip structure 600A forms a mesh-typearrangement for routing the body-bias voltage to surface N-well regionsso that pFETs can be body-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and first diagonal sub-surfacestrip structure 600A to provide a plurality of sub-surface conductivepaths between N-well regions without isolating P-well region locatedbetween N-wells. That is, first diagonal sub-surface strip structure600A contacts N-wells along the sub-surface conductive boundaries (e.g.,sub-surface conductive boundary 25 (FIG. 2A) and sub-surface conductiveboundaries 396 and 397 (FIG. 2B)).

As described above, the combination of surface N-well regions (e.g.,N-well_A, N-well_B, and N-well_C) and diagonal deep N-well regions610A-610D, which form the first diagonal sub-surface strip structure600A, facilitate the routing of the body-bias voltage Vnw to N-wellregions so that pFETs can be body-biased. First diagonal sub-surfacestrip structure 600A can be utilized in areas of the semiconductordevice that have a dense layout such as areas corresponding to an SRAM(static random access memory). It should be understood that firstdiagonal sub-surface strip structure 600A can have other configurations.Gap 640A between adjacent diagonal deep N-well regions can vary in size.Moreover, the ratio of diagonal deep N-well regions to gap area 630 canvary.

FIG. 6B illustrates a top view of multiple diagonal deep N-well (DDNW)regions forming a second diagonal sub-surface strip structure 600B inaccordance with an embodiment of the present invention. In this layoutpattern, each diagonal deep N-well region 612A-612D has a strip shape,is formed beneath the surface N-well layer of a semiconductor device,and is doped with an N-type material. Diagonal deep N-well regions612A-612D are formed in a second parallel orientation. The secondparallel orientation is diagonal (or slanted) with respect to surfaceN-well regions (e.g., N-well_D, N-well_E, and N-well_F). In anembodiment, the second parallel orientation and N-well regions form anangle that is approximately 45 degrees. In this case, the combination ofsurface N-well regions (e.g., N-well_D, N-well_E, and N-well_F) andsecond diagonal sub-surface strip structure 600B forms a mesh-typearrangement for routing the body-bias voltage to surface N-well regionsso that pFETs can be body-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and second diagonal sub-surfacestrip structure 600B to provide a plurality of sub-surface conductivepaths between N-well regions without isolating P-well region locatedbetween N-wells. That is, second diagonal sub-surface strip structure600B contacts N-wells along the sub-surface conductive boundaries (e.g.,sub-surface conductive boundary 25 (FIG. 2A) and sub-surface conductiveboundaries 396 and 397 (FIG. 2B)).

As described above, the combination of surface N-well regions (e.g.,N-well_D, N-well_E, and N-well_F) and diagonal deep N-well regions612A-612D, which form the second diagonal sub-surface strip structure600B, facilitate routing of the body-bias voltage Vnw to N-well regionsso that pFETs can be body-biased. Second diagonal sub-surface stripstructure 600B can be utilized in areas of the semiconductor device thathave a dense layout such as areas corresponding to an SRAM (staticrandom access memory). It should be understood that second diagonalsub-surface strip structure 600B can have other configurations. Gap 6408between adjacent diagonal deep N-well regions can vary in size.Moreover, the ratio of diagonal deep N-well regions to gap area 630 canvary.

FIG. 7 illustrates a top view of multiple axial deep N-well (ADNW)regions forming an axial sub-surface mesh structure 700 in accordancewith an embodiment of the present invention. As depicted in FIG. 7, eachaxial deep N-well region 710A-710E and 712A-712D has a strip shape, isformed beneath the surface N-well layer of a semiconductor device, andis doped with an N-type material. Axial deep N-well regions 710A-710Eare formed in a first parallel orientation while diagonal deep N-wellregions 712A-712D are formed in a second parallel orientation. The firstparallel orientation and the second parallel orientation are orthogonalto each other and are axially positioned with respect to N-well regionsof FIGS. 3A and 3B. That is, the first parallel orientation and thesecond parallel orientation are oriented along an axis (e.g., y-axis orx-axis) in the same manner as N-well regions of FIGS. 3A and 3B. In anembodiment, the first parallel orientation is parallel to N-well regionsof FIG. 3A and is perpendicular to N-well regions of FIG. 3B.Additionally, in an embodiment, the second parallel orientation isparallel to N-well regions of FIG. 3B and is perpendicular to N-wellregions of FIG. 3A. Thus, axial deep N-well regions 710A-710E and712A-712D form an axial sub-surface mesh structure 700 for routing thebody-bias voltage Vnw to N-well regions so that pFETs can bebody-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and axial sub-surface meshstructure 700 to provide a plurality of sub-surface conductive pathsbetween N-well regions without isolating P-well region located betweenN-wells. That is, axial sub-surface mesh structure 700 contacts N-wellsalong the sub-surface conductive boundaries (e.g., sub-surfaceconductive boundary 25 (FIG. 2A) and sub-surface conductive boundaries396 and 397 (FIG. 2B)).

It should be understood that axial sub-surface mesh structure 700 canhave other configurations. For example, gaps 740A and 740B betweenadjacent axial deep N-well regions can vary in size. Moreover, the ratioof axial deep N-well regions to gap area 730 can vary.

Additionally, axial sub-surface mesh structure 700 enables nFETS (n-typeMOSFETS) 380 (FIGS. 3A and 3B) to be body-biased in any manner bypreventing isolation of a P-type region or P-well region 385 (FIGS. 3Aand 3B) on which nFETS 380 are formed. Gap area 730 between axial deepN-well regions 710A-710E and 712A-712D prevents isolation of P-wellregion 385 and enables a conductive path between P-well region 385 and asub-surface layer that is beneath axial deep N-well regions 710A-710Eand 712A-712D. In an embodiment, the area of axial sub-surface meshstructure 700 is equally divided between axial deep N-well regions(e.g., 710A-710E and 712A-712D) and gap area 730.

As discussed above, a contact for the body-bias voltage Vnw can beformed wherever there is free space, such as above N-well regions orabove axial deep N-well regions 710A-710E and 712A-712D. Moreover, thelocation and size of axial sub-surface mesh structure 700 is based onthe distribution of N-wells and P-type regions or P-wells, wherein thegoal is to provide low resistance conductive paths for the body-biasvoltage Vnw.

As described above, the size of axial sub-surface mesh structure 700should avoid isolating P-type regions or P-wells 385 (FIGS. 3A and 3B)from sub-surface layers that are formed beneath axial deep N-wellregions 710A-710E and 712A-712D. Moreover, gap area 730 is sized so asto provide a low-resistance conductive path between P-type regions orP-wells 385 and a sub-surface layer that is formed beneath axial deepN-well regions, wherein the greater the gap area 730 the lower theresistance of this conductive path. Additionally, lateral diffusion andlateral depletion can further reduce gap area 730, potentiallypinching-off this conductive path between P-type regions or P-wells 385and a sub-surface layer that is formed beneath axial deep N-wellregions. As a solution to this situation, gaps 740A and 740B betweenadjacent axial deep N-well regions are made sufficiently wide to avoidpinching-off this conductive path between P-type regions or P-wells 385and a sub-surface layer that is formed beneath axial deep N-wellregions. Yet, as the number and size of the axial deep N-well regionsare increased, the resistance of the conductive path for routing thebody-bias voltage Vnw is decreased because there are larger and moresub-surface conductive boundaries between N-well regions and axial deepN-well regions. Hence, there is a trade-off between gap area 730 andaxial deep N-well regions in each design situation.

FIG. 8A illustrates a top view of multiple axial deep N-well (ADNW)regions forming a first axial sub-surface strip structure 800A inaccordance with an embodiment of the present invention. In this layoutpattern, each axial deep N-well region 810A-810D has a strip shape, isformed beneath the surface N-well layer of a semiconductor device, andis doped with an N-type material. Axial deep N-well regions 810A-810Dare formed in a first parallel orientation. The first parallelorientation is parallel to surface N-well regions (e.g., N-well_G,N-well_H, and N-well_I). In this case, the combination of surface N-wellregions (e.g., N-well_G, N-well_H, and N-well_I) and first axialsub-surface strip structure 800A forms a mesh-type arrangement forrouting the body-bias voltage to surface N-well regions so that pFETscan be body-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and first axial sub-surface stripstructure 800A to provide a plurality of sub-surface conductive pathsbetween N-well regions without isolating P-well region located betweenN-wells. That is, first axial sub-surface strip structure 800A contactsN-wells along the sub-surface conductive boundaries (e.g., sub-surfaceconductive boundary 25 (FIG. 2A) and sub-surface conductive boundaries396 and 397 (FIG. 2B)).

As described above, the combination of surface N-well regions (e.g.,N-well_G, N-well_H, and N-well_I), and axial deep N-well regions810A-810D, which form first axial sub-surface strip structure 800A,facilitate routing of the body-bias voltage Vnw to N-well regions sothat pFETs can be body-biased. First axial sub-surface strip structure800A can be utilized in areas of the semiconductor device that have adense layout and are oriented according to N-well regions of FIG. 3B. Itshould be understood that first axial sub-surface strip structure 800Acan have other configurations. Gap 840A between adjacent axial deepN-well regions can vary in size. Moreover, the ratio of axial deepN-well regions to gap area 830 can vary.

FIG. 8B illustrates a top view of multiple axial deep N-well (ADNW)regions forming a second axial sub-surface strip structure 800B inaccordance with an embodiment of the present invention. In this layoutpattern, each axial deep N-well region 812A-812D has a strip shape, isformed beneath the surface N-well layer of a semiconductor device, andis doped with an N-type material. Axial deep N-well regions 812A-812Dare formed in a second parallel orientation. The second parallelorientation is parallel to surface N-well regions (e.g., N-well_J,N-well_K, and N-well_L). In this case, the combination of surface N-wellregions (e.g., N-well_J, N-well_K, and N-well_L) and second axialsub-surface strip structure 800B forms a mesh-type arrangement forrouting the body-bias voltage to surface N-well regions so that pFETscan be body-biased.

As described above with respect to FIGS. 2A and 2B, the layercorresponding to the deep N-well region is below the layer correspondingto the surface N-well regions. Hence, sub-surface conductive boundariescan be formed between N-well regions and second axial sub-surface stripstructure 800B to provide a plurality of sub-surface conductive pathsbetween N-well regions without isolating P-well region located betweenN-wells. That is, second axial sub-surface strip structure 800B contactsN-wells along the sub-surface conductive boundaries (e.g., sub-surfaceconductive boundary 25 (FIG. 2A) and sub-surface conductive boundaries396 and 397 (FIG. 2B)).

As described above, the combination of surface N-well regions (e.g.,N-well_J, N-well_K, and N-well_L), and axial deep N-well regions812A-812D, which form second axial sub-surface strip structure 800A,facilitates routing of the body-bias voltage Vnw to N-well regions sothat pFETs can be body-biased. Second axial sub-surface strip structure800B can be utilized in areas of the semiconductor device that have adense layout and are oriented according to N-well regions of FIG. 3A. Itshould be understood that second axial sub-surface strip structure 800Bcan have other configurations. Gap 840B between adjacent axial deepN-well regions can vary in size. Moreover, the ratio of axial deepN-well regions to gap area 830 can vary.

Structure for Spanning Gap in Deep N-Well Structure for RoutingBody-Bias Voltage

As noted above, the following description of the present invention isequally applicable to a p-type substrate and an N-well process, as wellas to an n-type substrate and a P-well process.

As described above, the deep N-well region can have many differentlayout patterns for routing the body-bias voltage. Examples of theselayout patterns include a diagonal sub-surface mesh structure (FIGS. 5Aand 5B), an axial sub-surface mesh structure (FIG. 7), a diagonalsub-surface strip structure (FIGS. 6A and 6B), and an axial sub-surfacestrip structure (FIGS. 8A and 8B).

When a deep N-well structure is utilized to route the body-bias voltage,there are occasions when the deep N-well structure may be interrupted orseparated in multiple sections by an isolation structure. Ideally, thedeep n-well structure should not contact or cross the isolationstructure because short circuit conditions can be created. Thisisolation structure is used for nFETs and/or pFETs that form specializedcircuits (e.g., I/O circuits, analog circuits, etc.) requiring voltagesthat are different than the voltages provided to core region nFETs andpFETs. Typically, the isolation structure has a strip configuration ofvarious lengths. It should be understood that the isolation structurecan also be a deep N-well structure having a voltage bias that isdifferent than the voltage bias of another deep N-well structure.

For isolating nFETs, the isolation structure is comprised of acontinuous (surface) N-well perimeter and a solid deep N-well platestructure, forming a p-type isolation tub. For isolating pFETs, theisolation structure is comprised of a separate (surface) N-well.Moreover, the isolation structure can be configured for isolating bothnFETs and pFETs. In this case, one or more perimeter sides of thecontinuous (surface) N-well perimeter of the isolation structure canhelp form the isolated pFETs.

Although the discussion below will focus on deep N-well mesh structures(e.g., diagonal sub-surface mesh structure (FIGS. 5A and 5B)), thediscussion is equally applicable to other deep N-well structuresutilized to route the body-bias voltage.

FIG. 9A illustrates a top view of a semiconductor device 100, showing afirst deep N-well mesh structure 10, a second deep N-well mesh structure20, and an isolation structure 70 formed between deep N-well meshstructures 10 and 20 to create a gap between deep N-well mesh structures10 and 20 in accordance with an embodiment of the present invention. Asdepicted in FIG. 9A, isolation structure 70 created a gap 15 in a deepN-well mesh structure 50, wherein gap 15 separated deep N-well meshstructure 50 into first deep N-well mesh structure 10 and second deepN-well mesh structure 20. Here, deep N-well mesh structure 50 is adiagonal deep N-well mesh structure. Deep N-well mesh structure 50 iscomprised of a plurality of diagonal deep N-well regions 52.

FIG. 9B illustrates a top view of a semiconductor device 100, showing adeep N-well mesh structure 50 and an isolation structure 70 that createsa gap 15 in deep N-well mesh structure 50 in accordance with anembodiment of the present invention As depicted in FIG. 9B, isolationstructure 70 created a gap 15 in a deep N-well mesh structure 50,wherein gap 15 interrupts deep N-well mesh structure 50 rather thanseparating it. Isolation structure 70 is formed within the perimeter ofdeep N-well mesh structure 50. Here, deep N-well mesh structure 50 is adiagonal deep N-well mesh structure. Deep N-well mesh structure 50 iscomprised of a plurality of diagonal deep N-well regions 52.

Referring to FIGS. 9A and 9B, isolation structure 70 includes an N-wellperimeter 74 and a solid deep N-well plate structure 25 (see FIG. 10),forming a p-type isolation tub 76. Isolation structure 70 is utilized toform specialized circuits (e.g., I/O circuits, analog circuits, etc.),as described above.

Gap 15 interrupts the routing of body-bias voltage. However, if the areaof gap 15 is sufficiently large to negatively affect the electricalresistance property of deep N-well mesh structure 50, corrective actionhas to be taken to reduce the impact of gap 15 (due to isolationstructure 70) on the electrical resistance property of deep N-well meshstructure 50. As will be described below, at least one metal structure80 (see FIGS. 11A and 11B) is formed across the isolation structure 70to address the impact of gap 15 (due to the isolation structure 70) onthe electrical resistance property of the deep N-well mesh structure 50.Metal structure 80 (see FIGS. 11A and 11B) is coupled to deep N-wellmesh structure 50 with tap contacts on opposite sides of isolationstructure 70.

FIG. 10 illustrates a cross-sectional view of semiconductor device 100of FIG. 9A along line A-B in accordance with an embodiment of thepresent invention. Deep N-well mesh structure 50 (see FIG. 9A) is formedbelow surface 90. As shown in FIG. 10, isolation structure 70 includesan N-well perimeter 74 and a solid deep N-well plate structure 25,forming a p-type isolation tub 76. Gap 15 separates deep N-well meshstructure 50 (see FIG. 9A) into first deep N-well mesh structure 10 andsecond deep N-well mesh structure 20. First deep N-well mesh structure10 does not contact isolation structure 70. Additionally, second deepN-well mesh structure 20 does not contact isolation structure 70. Thefirst and second deep N-well mesh structures 10 and 20 are comprised ofa plurality of diagonal deep N-well regions 52.

It should be understood that regions 94 and 96 are utilized to formnFETs and pFETs described in FIGS. 1-8B.

FIG. 11A illustrates a top view of semiconductor device 100 of FIG. 9A,showing a metal structure 80 for spanning isolation structure 70 inaccordance with an embodiment of the present invention. Similarly, FIG.11B illustrates a top view of semiconductor device 100 of FIG. 9B,showing a metal structure 80 for spanning isolation structure 70 inaccordance with an embodiment of the present invention.

Referring to FIGS. 11A and 11B, at least one metal structure 80 isutilized to span isolation structure 70. Metal structure 80 carrieselectrical current across isolation structure 70. While in FIG. 11A tapcontact 81 couples metal structure 80 to first deep N-well meshstructure 10, tap contact 81 couples metal structure 80 to deep N-wellmesh structure 50 in FIG. 11B. Moreover, while in FIG. 11A tap contact82 couples metal structure 80 to second deep N-well mesh structure 20,tap contact 82 couples metal structure 80 to deep N-well mesh structure50 in FIG. 11B. In an embodiment, metal structure 80 has a metal wireshape. It should be understood that metal structure 80 can have othershapes. For example, the portion of metal structure 80 that overlapsdeep N-well structure 10 (FIG. 11A), 20 (FIG. 11A), and 50 (FIG. 11B)can have a T-shape. This enables the formation of additional tapcontacts from metal structure 80 to deep N-well structure 10 (FIG. 11A),20 (FIG. 11A), and 50 (FIG. 11B). This provides lower resistance betweenmetal structure 80 and deep N-well structure 10 (FIG. 11A), 20 (FIG.11A), and 50 (FIG. 11B).

Metal structure 80 can be comprised of a single metal layer.Alternatively, metal structure 80 can be comprised of a plurality ofmetal layers. Furthermore, the number of metal structures 80 needed isdependent on several factors. These factors include the sheet resistanceof deep N-well mesh structure, the sheet resistance of metal structure80, and the width 83 of isolation structure 70.

In an embodiment, a deep N-well plate 51 (FIG. 11A and FIG. 11B) can beformed beneath metal structure 80 where tap contacts 81 and 82 arelocated. The deep N-well plate 51 is a continuous sub-surface layerrather than a sub-surface patterned layer as described in FIGS. 1-11Bwith respect to deep N-well structures for routing body-bias voltage.Each deep N-well plate 51 is coupled to deep N-well structure 10 (FIG.11A), 20 (FIG. 11A), and 50 (FIG. 11B). Thus, lower resistance betweenmetal structure 80 and deep N-well structure 10 (FIG. 11A), 20 (FIG.11A), and 50 (FIG. 11B) is achieved. In an embodiment, deep N-wellplates 51 are diagonally oriented (or rotated with respect to theposition shown in FIGS. 11A and 11B) to provide greater intersectionbetween deep N-well structure and deep N-well plate 51.

The values provided henceforth to determine the benefits of using metalstructure 80 are illustrative. The present invention is not limited tothese values. The values may be different in other cases for numerousreasons (e.g., manufacturing process utilized, materials utilized,etc.). The sheet resistance of deep N-well region is approximately 1000ohms per square. The sheet resistance of deep N-well mesh structure 50is approximately 2000 ohms per square. The sheet resistance of a metalsheet is approximately 0.2 ohms per square. The goal is to supplysufficient metal structure(s) to improve the resistance property of deepN-well mesh structure 50 having gap 15.

In an embodiment, the width of metal structure 80 is approximately 1 μm(or 1 unit) wide, wherein μm represents micrometers. Moreover, a metalstructure 80 is placed approximately every 1000 μm or (1000 units),wherein μm represents micrometers. Thus, the sheet resistance of metalstructure 80 is approximately 200 ohms per square (0.2.times.1000),since metal structure 80 (of approximately 1 μm width) is placedapproximately every 1000 μm. Since the sheet resistance of a metal sheetis approximately 1000 times lower (or better) than the sheet resistanceof deep N-well mesh structure 50, metal structure(s) 80 have no moreelectrical resistance than the electrical resistance of the portion ofdeep N-well mesh structure 50 that could occupy the area of gap 15.

Moreover, since metal structure 80 is placed every 1000 μm, thecapacitance of metal structure(s) 80 does not appreciably increase thecapacitance of deep N-well mesh structure 50. Thus, metal wire to metalwire coupled noise on metal structure 80 does not significantlycontribute to body-bias voltage noise (or substrate noise).

Alternatively, metal structure 80 can be replaced with structurescomprised of polysilicon wiring, diffusion wiring, or silicide wiring.However, these alternative implementations are less beneficial thanusing metal structure 80. Higher sheet resistance and a larger number ofthese structures formed across the isolation structure characterizethese alternative implementations.

The above discussion focused on deep N-well mesh structures (e.g.,diagonal sub-surface mesh structure of FIGS. 5A and 5B). However, theabove discussion is equally applicable to other deep N-well structuresutilized to route the body-bias voltage.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and many modifications andvariations are possible in light of the above teaching. The embodimentswere chosen and described in order to best explain the principles of theinvention and its practical application, to thereby enable othersskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the Claims appended hereto and their equivalents.

What is claimed is:
 1. A semiconductor device comprising: two conductiveregions of a first conductivity type formed beneath a surface of thesemiconductor device, wherein the two conductive regions are configuredto route a body-bias voltage, and wherein the two conductive regions donot reach the surface; and a metal structure formed above the surface,wherein the metal structure is coupled to the two conductive regions. 2.The semiconductor device of claim 1, wherein each conductive region hasan N-type doping.
 3. The semiconductor device of claim 1, wherein eachconductive region has a P-type doping.
 4. The semiconductor device ofclaim 1, wherein each conductive region has a strip shape.
 5. Thesemiconductor device of claim 1, wherein the metal structure has a metalwire shape.
 6. The semiconductor device of claim 1, wherein the metalstructure passes over a region of a second conductivity type.
 7. Asemiconductor device comprising: two deep wells of a first conductivitytype, wherein each deep well is formed beneath a surface of thesemiconductor device, wherein the two deep wells are operable to route abody-bias voltage, and wherein the two deep wells do not reach thesurface; two other deep wells of the first conductivity type, whereineach of the two other deep wells is formed beneath the surface, whereinthe two other deep wells are operable to route the body-bias voltage,wherein the two other deep wells do not reach the surface, and whereinthe two other deep wells are physically separate; and a conductivestructure formed above the surface, wherein the conductive structurecouples at least one of the two deep wells and at least one of the twoother deep wells.
 8. The semiconductor device of claim 7, wherein eachdeep well has an N-type doping.
 9. The semiconductor device of claim 7,wherein each deep well has a P-type doping.
 10. The semiconductor deviceof claim 7, wherein at least one of the deep wells has a strip shape.11. The semiconductor device of claim 7, wherein the conductivestructure has a metal wire shape.
 12. The semiconductor device of claim7, wherein the conductive structure passes over a well of a secondconductivity type.
 13. A semiconductor device comprising: two conductiveregions of a first conductivity formed beneath a surface of thesemiconductor device, wherein the two conductive regions are configuredto route a body-bias voltage, and wherein the two conductive regions donot reach the surface; and a conductive structure above the surface thatis coupled to the two conductive regions.
 14. The semiconductor deviceof claim 13, wherein each conductive region has an N-type doping. 15.The semiconductor device of claim 13, wherein each conductive region hasa P-type doping.
 16. The semiconductor device of claim 13, wherein eachconductive region has a strip shape.
 17. The semiconductor device ofclaim 13, wherein the conductive structure is a polysilicon wire. 18.The semiconductor device of claim 13, wherein the conductive structureis a diffusion wire.
 19. The semiconductor device of claim 13, whereinthe conductive structure is a silicide wire.
 20. The semiconductordevice of claim 13, wherein each of the conductive regions has acontinuous sub-surface layer shape.